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Characterization of Cryogenic Solid Hybrid Rocket Motors.

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Technical paper,

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The study of the combustion of cryogenic 77K solid hydrocarbons in a laboratory scale tube burner that approximates the geometry of the hybrid rocket was extended. This work was carried out to demonstrate the feasibility of cryogenic fuel combustion in the hybrid rocket geometry and to extend knowledge about hybrid rockets to fuels that have very high regression rates as a consequence of their high mass transfer number, or blowing coefficient. Liquid n-pentane was condensed inside a 1-inch diameter tube that was cooled by liquid nitrogen. A mandrel was used to shape a 6-inch long by 1-inch diameter solid fuel grain with a one-half-inch diameter channel along the centerline the mass of the n-pentane fuel grain was around 35 grams. These fuel samples were ignited with a methaneoxygen microtorch and burned with gaseous oxygen GOX, up to 25 gramssec under conditions of choked flow. Combustion pressure Pc, up to 250 psia depends on the throat area of the choke, a converging sonic nozzle. Pc also depends on the fuel, the mass flow rates of fuel and GOX, and the oxidation efficiency. Burn times varied between 1 and 8 seconds. Images of the turbulent reacting boundary layer and burning fuel surface and of the exit plume were recorded with a CCDvideo system. Two figures of merit were determined the instantaneous fuel regression rate rt cmsec and the instantaneous characteristic velocity csolid start cmsec, the metric of combustion efficiency achieved during combustion. Lower pressure experiments burned with a low oxidizer to fuel mass ratio OF around unity and considerable sooting these large r burns were accompanied by low Csolid star combustion efficiency, as low as 50 of Csolid starideal.

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  • Rockets

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